强流离子束在固体等离子体靶输运的混合粒子模拟方法

doi:10.19596/j.cnki.1001-246x.8609

摘要/Abstract

摘要：

针对强流离子束在固体等离子体靶中的输运问题, 详细介绍一种粒子/流体混合模拟方法, 发展了二维数值模拟程序Opic2D-hybrid, 研究强流质子束在聚乙烯和固态铝靶中的集体输运行为。结果表明: 强流质子束在固体靶中输运时产生的自生磁场有利于横向箍缩质子束流。并且靶加热离化产生的大量自由电子, 也有利于减弱固体靶的阻止本领, 从而拉长质子束流射程。但是靶温度升高也会降低电阻率, 抑制自生磁场产生。同时靶离化也会带来更强的离子-离子散射效应, 导致质子束的空间扩散。这些效应彼此间相互竞争, 决定了强流质子束的输运行为。还分析了影响磁场产生的物理因素, 提出多种手段提高自生磁场强度, 从而实现强流质子束在固体靶中的箍缩传输。

关键词: 强流离子束输运, 混合粒子模拟, 自生磁场, 阻止本领

Abstract:

A hybrid particle-in-cell/fluid method is introduced to simulate the transport of intense ion beams in the solid plasmas. A two-dimensional numerical program opic2d-hybrid has been developed and it is used to study the collective behavior of the intense proton beam transport into the polyethylene and solid aluminum targets. It is shown that intense magnetic field is self-generated by the transport of intense proton beam in solid targets. This magnetic field is of benefit to pinch the proton beam. Moreover, due to the production of substantial free-electrons by the target heating and ionization, the stopping power of solid target become weaken, thereby lengthening the proton beam range. On the contrary, the increase of target temperature will reduce the resistivity and thus inhibit the generation of magnetic field. Furthermore, the target ionization leads to much stronger ion-ion scattering effect, thus resulting in the diffusion of protons in transverse space. These effects compete with each other and determine the transport behavior of intense proton beam. At the last, the physical factors contributing to the generation of magnetic field are also analyzed. Some means to increase the strength of magnetic field have been proposed in order to realize the pinch transport of intense proton beams in solid targets.

Key words: intense ion beam transport, hybrid particle-in-cell/fluid simulation, self-generated magnetic field, stopping power

张智猛, 齐伟, 崔波, 张博, 洪伟, 周维民. 强流离子束在固体等离子体靶输运的混合粒子模拟方法[J]. 计算物理, 2023, 40(2): 210-221.

Zhimeng ZHANG, Wei QI, Bo CUI, Bo ZHANG, Wei HONG, Weimin ZHOU. Hybrid Particle-in-cell/Fluid Method for Intense Ion Beam Transport in Solid Plasmas[J]. Chinese Journal of Computational Physics, 2023, 40(2): 210-221.

图/表 5

图1 固体铝Al和聚乙烯CH2的(a)平均离化度和(b)电阻率(固体铝Al的材料常数ks =Av =0.2；聚乙烯CH2，ks =2, Av =10。)

Fig.1 (a) Averaged ionization and (b) resistivity of solid aluminum Al and polyethylene CH2 (Here ks =Av =0.2 are adopted for Al while they are ks =2 and Av =10 for CH2.)

图2 在30 ps时刻，5 MeV准直质子束入射到CH2靶中的角向磁场Bθ和靶温度Te分布，质子束电流密度：(a)~(b) 109 A·cm-2，(c)~(d) 1011 A·cm-2，(e)~(f) 1013 A·cm-2

Fig.2 The spatial distribution of the magnetic field Bθ and the target temperature Te at t=30 ps, which are caused by the 5 MeV collimated proton beam propagates into the solid CH2 target. The proton current densities are (a)~(b) 109 A·cm-2, (c)~(d) 1011 A·cm-2 and (e)~(f) 1013 A·cm-2

图3 在30 ps时刻，5 MeV准直质子束入射到Al靶中的角向磁场Bθ和靶温度Te分布，质子束电流密度：(a)~(b) 109 A·cm-2，(c)~(d) 1011 A·cm-2，(e)~(f) 1013 A·cm-2

Fig.3 The spatial distribution of the magnetic field Bθ and the target temperature Te at f = 30 ps, which are caused by the 5 MeV collimated proton beam propagates into the solid Al target. The proton current densities are (a)~(b) 109 A·cm-2, (c)~(d) 1011 A·cm-2 and (e)~(f) 1013 A·cm-2

图4 在30 ps时刻，10 MeV准直质子束入射到靶中的角向磁场Bθ和靶温度Te分布。(束腰半径w = 10 μm)(a)~(b) CH2靶；(c)~(d) Al靶

Fig.4 The spatial distribution of the magnetic field Bθ and the target temperature Te at t = 30 ps, which are caused by the 10 MeV collimated proton beam propagates into the solid targets. The proton beam has a waist of 10 μm. The target materials are (a)~(b) CH2 and (c)~(d) Al.

图5 在30 ps时刻，5 MeV准直质子束入射到靶中的角向磁场Bθ和靶温度Te分布(质子束电流密度为1011 A·cm-2，束腰半径w = 5 μm) (a)~(b) CH2靶；(c)~(d) Al靶

Fig.5 The spatial distribution of the magnetic field Bθ and the target temperature Te at t = 30 ps, which are caused by the 5 MeV collimated proton beam propagates into the solid targets. The proton beam has a current density of 1011 A·cm-2 and a waist of 5 μm. The target materials are (a)~(b) CH2 and (c)~(d) Al.

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